In order to meet the increasing demand for wireless data traffic since the commercialization of 4th generation (4G) communication systems, the development focus is on the 5th generation (5G) or pre-5G communication system. For this reason, the 5G or pre-5G communication system is called a beyond 4G network communication system or post long-term evolution (LTE) system. Consideration is being given to implementing the 5G communication system in millimeter wave (mmWave) frequency bands (e.g., 60 GHz bands) to accomplish higher data rates. In order to increase the propagation distance by mitigating propagation loss in the 5G communication system, discussions are underway about various techniques such as beamforming, massive multiple-input multiple output (MIMO), full dimensional MIMO (FD-MIMO), array antenna, analog beamforming, and large-scale antenna. Also, in order to enhance network performance of the 5G communication system, developments are underway of various techniques such as evolved small cell, advanced small cell, cloud radio access network (RAN), ultra-dense network, device-to-device (D2D) communication, wireless backhaul, moving network, cooperative communication, coordinated multi-points (CoMP), and interference cancellation. Furthermore, the ongoing research includes the use of hybrid frequency shift keying (FSK) and quadrature amplitude modulation (QAM){FQAM} and sliding window superposition coding (SWSC) as advanced coding modulation (ACM), filter bank multi-carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA).
Meanwhile, the Internet is evolving from a human-centric communication network in which information is generated and consumed by humans to the Internet of things (IoT) in which distributed things or components exchange and process information. The combination of the cloud server-based Big data processing technology and the IoT begets Internet of everything (IoE) technology. In order to secure the sensing technology, wired/wireless communication and network infrastructure, service interface technology, and security technology required for implementing the IoT, recent research has focused on sensor network, machine-to-machine (M2M) communication, and machine-type communication (MTC) technologies. In the IoT environment, it is possible to provide an intelligent Internet Technology that is capable of collecting and analyzing data generated from connected things to create new values for human life. The IoT can be applied to various fields such as smart home, smart building, smart city, smart car or connected car, smart grid, health care, smart appliance, and smart medical service through legacy information technology (IT) and convergence of various industries.
Thus, there are various attempts to apply the IoT to the 5G communication system. For example, the sensor network, M2M communication, and MTC technologies are implemented by means of the 5G communication technologies such as beamforming, MIMO, and array antenna. The application of the aforementioned cloud RAN as a big data processing technology is an example of convergence between the 5G and IoT technologies.
The mobile communication system has evolved to broadband wireless communication systems for supporting high-speed, high-quality wireless packet data services beyond the early voice-oriented services on the basis of communication standards such as high-speed packet access (HSPA) of the 3rd generation partnership project (3GPP), long term evolution (LTE) or evolved universal terrestrial radio access (E-UTRA), high rate packet data (HRPD) of the 3GPP2, ultra-mobile broadband (UMB), and 802.16e of the Institute of Electrical and Electronics Engineers (IEEE).
The LTE system as one of the representative broadband wireless communication systems uses orthogonal frequency division multiple access (OFDMA) in the downlink and single carrier frequency division multiple access (SC-FDMA) in the uplink. Such a multiple access scheme is characterized by allocating the time-frequency resources for transmitting user-specific data and control information without overlap of each other, i.e. maintaining orthogonality, so as to distinguish among user-specific data and control information.
The LTE system adopts a Hybrid Automatic Repeat Request (HARQ) scheme for physical layer retransmission when decoding failure occurs in initial data transmission. The HARQ scheme is designed to operate in such a way that a receiver that fails in decoding data sends a transmitter a negative acknowledgement (NACK) indicative of decoding failure in order for the transmitter to retransmit the corresponding data on the physical layer. The receiver combines the retransmitted data with the decoding-failed data to improve data reception performance. It may also be possible for the receiver to send the transmitter an Acknowledgement (ACK) indicative of successful decoding, when the data are decoded successfully, in order for the transmitter to transmit new data.
The LTE system also adopts a channel state-adaptive resource allocation scheme to improve downlink reception performance of a terminal. The base station transmits channel state information-reference signal (CSI-RS) in downlink for the purpose of channel-adaptive resource allocation to the terminal That is, the terminal performs channel measurement on the CSI-RS to generate channel quality information (CQI) and transmits the CQI to the base station. The base station may allocate best frequency resources to the terminal based on the CQI.